Emission Decay Research Articles

Photophysics of Hydrophobic Corroles in the Aqueous Micellar Media and in the Presence of Graphene Oxide and Bioanalytes.

Here two A2B type corrole has been synthesized and solubilized in water via pluronic micelle system by avoiding the utmost mandatory multistep non-environment friendly strategies for bringing hydrophobic non-ionic corroles in aqueous medium. Both the corroles were extremely insoluble in water as no absorption spectra of corrole was available in water. However, corrole 2 in the aqueous solution of F127 exhibit characteristic Soret and Q bands due to efficient solubilization of corrole in F127, the micelles formed by block copolymer act as a "cargo hold" for the corrole molecules. Intense emission spectra were observed for both the corroles in the aqueous solution of F127. We further observed that fluorescence properties of corrole-F127 micelle systems are quenched in presence of graphene oxide (GO) without change in the wavelength or shape of the emission band. The possibility of a dynamic quenching is probed more quantitatively by recording the emission decay profiles of corrole-F127-GO system. This quenching of fluorescence intensity of graphene oxide dispersed corrole-F127 micellar system was partially re-established in the presence of bioanalytes such as dopamine, ascorbic acid. Therefore, the present work has a future potential application for analyzing the interaction with different bioanalytes in biological systems using corrole-GO composite.

Lifetime, size and emission of laser-induced plasmas for in-situ laser-induced breakdown spectroscopy on Earth, Mars and Moon

The spectroscopic technique of laser-induced breakdown spectroscopy (LIBS) is a powerful method to perform rapid chemical analysis of geologic samples with short measurement times and no need for sample preparation. After the ChemCam instrument aboard NASA’s MSL rover proved its suitability for space missions that explore planetary surfaces in 2012, the interest in LIBS instruments as payloads has grown and several subsequent missions have successfully used this technique since. The characteristics of a LIBS plasma depend on experimental and environmental parameters as well as on sample properties, including atmospheric conditions, laser irradiance and sample lithology. Consequently, LIBS instruments need to be designed and optimized specifically for each use case to maximize their science output. To aid in the development of new LIBS instruments for space exploration, we investigate the influence of atmospheric conditions, laser irradiance and sample lithology on the lifetime, size and emission of laser-induced plasmas. In our measurements, we use a plasma imaging setup with high temporal resolution of down to 2ns to investigate the evolution of the plasma from its ignition to its decay. We present a comparable data set recorded at terrestrial, Martian and airless atmospheric conditions, covering irradiances between 0.79GW/mmˆ2 and 1.43GW/mmˆ2 and samples with diverse properties, namely basalt and soapstone, as well as the lunar regolith simulants LHS-1 and LMS-1. Our measurements show the strong influence of atmospheric conditions on the plasma size and emission, while the lithologies and laser irradiances covered in this work play a minor role. This shows that instruments designed to work at certain atmospheric conditions can be used for a range of laser parameters and sample properties. Furthermore, we demonstrate that the decay of the plasma emission and the expansion of the plasma plume parallel to the sample surface can be described well by a power law and a drag model, respectively.

High Reverse Intersystem Crossing Rate Diminishes the Impact of Conformational Disorder Phenomenon in Solid‐State TADF

AbstractEmbedding donor–acceptor type thermally activated delayed fluorescence (TADF) molecules in a rigid surrounding lead to structural inhomogeneity, and deteriorating emission decay rates. Designing TADF structures with hampered rotational flexibility between donor and acceptor structural units is shown to lower the conformational disorder. However, in this work, it is shown that it is not always enough. In fact, the negative impact of conformational inhomogeneity may be reduced by lowering the singlet‐triplet energy gap (ΔEST) and boosting the reverse intersystem crossing (rISC) rate while preserving the same donor‐acceptor orientation. In such cases the lower ΔEST enables the early triplet upconversion even from the conformers with unfavorably low D‐A twist angles, which is not observed in compounds with larger ΔEST. In this way, the temporal shifts of prompt and delayed fluorescence are evidently reduced. When the reverse intersystem crossing is inactive at low temperatures, nearly the same fluorescence peak shifts are observed, as expected for compounds with similar molecular geometry. In this way, low ΔEST and rapid rISC are shown to be of fundamental importance not only for TADF efficiency but also for the temporal dynamics in the solid‐state.

Could organoaluminium complexes act as prominent TADF emitters for designing efficient diode devices? A DFT/TDA simulation study

Theoretical calculations suggest possible designs of Thermally Activated Delayed Fluorescence (TADF) emitters using three-coordinate aluminium (Al-X3) complexes for the design of organometal light emitting diodes. We investigate the optical properties of gas-phase and toluene-solvated Ac-Al, Ac-Al-F, Ac-Al-CN and Ac-Al-NO2 complexes using DFT/TDA methods. All calculations were carried out using the long-range corrected ωB97XD functional with optimal ω values. Except for Ac-Al-CN contender, the aluminum atom has magnified the spin–orbit couplings between the excited singlet (S1) and triplet (T1) states. The decrease in the reorganization energies of Ac-Al-CN and Ac-Al-NO2 complexes has maximized their reverse intersystem crossing rate constants. The presence of the strong electron withdrawing nitro group has further stabilized its LUMO together with improving both its oscillator strength and the emission decay rate constant. This contender is predicted to be the most prominent TADF emitter and highly promising for designing diode devises amongst the understudy complexes.

Growth and spectroscopy characteristics of Er, Ce:BGSO crystal: A promising material for eye-safe laser applications

Er, Ce co-doped BGSO single crystals were successfully grown by the Bridgman method. The growth parameters, including temperature gradient and growth rate, were optimized to achieve high-quality crystals. The crystal structure and morphology were characterized using X-ray diffraction and scanning electron microscopy. The optical absorption properties of Er, Ce co-doped BGSO single crystals were studied using UV–Vis absorption spectroscopy. The absorption spectrum revealed the absorption edge and the presence of absorption bands related to the presence of Ce dopant, providing valuable insights into the energy transfer processes occurring within the crystal lattice. Furthermore, the luminescence mechanism of BGSO crystals was analyzed using the Judd-Ofelt (J-O) theory, with detailed investigation into the role of ligands in spectral parameters. The photoluminescence spectra and emission decay time of Er, Ce co-doped BGSO single crystals were characterized. A comparative analysis with Er, Ce:BGSO crystals was conducted to investigate the sensitization mechanism of Ce ions on Er emission at 1.5 μm, demonstrating their potential for use as eye-safe laser materials in various applications.

Enhancement of Circularly Polarized Luminescence Brightness of Schiff‐Base Diphenylboron and 9‐Borafluoren‐9‐yl Complexes

AbstractA series of diphenylboron and 9‐borafluoren‐9‐yl complexes with chiral Schiff‐base ligands was synthesized and characterized by NMR spectroscopy. X‐ray diffraction analysis revealed that their boron centers were adapted to tetrahedral coordination geometry. Although boron complexes with salicylideneimine backbones exhibited a weak circularly polarized luminescence (CPL), the CPL brightness (BCPL) was enhanced more than 9‐fold by the π‐extension of the Schiff base ligands. Time‐resolved emission decay analysis and theoretical calculations based on density functional theory (DFT) were conducted to further understand their luminescent properties.

Colloidal down-shifting Gd2O3:Eu3+/SiO2 phosphors nanocomposites using one-pot modified surfactants-based soft templates for catalytic applications

The application of rare earth (RE)-based phosphor materials faces a significant challenge in adopting strategies to bring down the cost without compromising their properties. The most straightforward approach is to minimize the use of RE elements. Herein, we demonstrate the use of SiO2 as an economical solid nano-matrix for lanthanides-based phosphor nanomaterials. Gd2O3:Eu3+(x%) and Gd2O3:Eu3+(x%)/SiO2 nanophosphor composites were prepared through a modified soft templating technique using cetyltrimethylammonium bromide (CTAB) as the surfactant. The photoluminescence properties were studied by excitation, emission, and luminescence decay investigations. Upon excitation in the O2−(2p)→Eu3+(4f6) LMCT state, these nanophosphors exhibited predominantly red emission from the 5D0→7FJ transition (where J = 0–4) of the Eu3+ ion. Moreover, the synthesized low-cost Gd2O3Eu3+(5 %)/SiO2 composites, with a small number of lanthanides, exhibited excellent photocatalytic degradation activity for organic dye (methylene blue) under visible light (λ ≥ 420 nm), showing promising potential for photocatalytic wastewater treatment.

Insights into the Structural, Thermal/Dilatometric, and Optical Properties of Dy3+-Doped Phosphate Glasses for Lighting Applications.

Dysprosium-doped glasses are of interest for applications in light-emitting devices, yet the full range of effects of Dy3+ ions on glass properties is not fully understood. In this work, phosphate glasses with 50P2O5-(50 - x)BaO-xDy2O3 (0 ≤ x ≤ 4.0 mol %) nominal compositions were prepared by melting and the impact of Dy3+ ions on glass physical, structural, thermo-mechanical, and optical properties was evaluated. Following refractive index, density, and X-ray diffraction characterizations, the glasses were studied comprehensively through Raman spectroscopy, X-ray photoelectron spectroscopy, dilatometry, optical absorption, and photoluminescence (PL) spectroscopy. The thorough investigation and data analyses shed light on the Dy3+-driven structural and thermal properties reported here for the first time. The thermal expansion behavior was put in context with the reported data for other lanthanides and analyzed in the framework of the high ionic field strengths, leading to tighter glass networks. Further, a detailed analysis of the absorption, PL, and emission decay curves was carried out, providing insights into the origin of the optical behavior. Supported is the hypothesis that the cross-relaxation channels between Dy3+ ions taking place at low concentrations are responsible for the decrease in the decay times while the PL attractive for lighting applications still improves. Conversely, high Dy3+ concentrations facilitate the emission quenching proceeding via an electric dipole-dipole interaction likely incorporating the resonant excitation migration pathway for Dy3+-Dy3+ mean distances shorter than ∼15 Å.

Luminescence and Faraday rotation properties of Tb2O3 and Tb:Y2O3 single crystals

Heavily-doped and fully concentrated 2.78 % Tb:Y2O3 and Tb2O3 single crystals with high optical quality and very low levels of impurities have been grown and studied for their luminescence and Faraday rotation properties. Absorption, emission and fluorescence decay measurements performed vs excitation wavelength and temperature and their confrontation with Judd-Ofelt and crystal-field calculations show the contributions of two types of luminescent centers: dominant ones with a 5D4 emission lifetime of 23 μs corresponding to coupled near-neighbor Tb3+ ions, all in C2 symmetry sites, and minority ones with a 5D4 emission lifetime of about 2 ms corresponding to coupled Tb3+ ions in C2 and C3i near-neighbor symmetry sites. Faraday rotation measurements confirm Tb2O3 as the Tb-based Faraday crystalline material with the largest ever measured Verdet constant, at all temperatures and from the visible to the near-infrared. They also show that the dominant luminescent centers contribute more particularly to this large Verdet constant thanks to a favorable crystal-field splitting of their 7F6 ground multiplet and also to the contributions of both types of spin-allowed and spin-forbidden 4f-5d absorption bands.

Energy Transfer of a New Self-Activating Ba<sub>3</sub>TaGa<sub>3</sub>Si<sub>2</sub>O<sub>14</sub>: ySm<sup>3+</sup>, xNb<sup>5+</sup> Phosphor Obtained by a Small Substitution of Nb<sup>5+</sup> for Ta<sup>5+</sup>

Self-activated multicolor phosphors are being used in more and more emerging fields. In order to explore the energy transfer between [NbO6]7- coordination groups and Sm3+ ions, a series of Ba3-ySmyTa1-xNbxGa3Si2O14 samples co-doped with Nb5+ and Sm3+ were prepared in this work, and the changes of luminous intensity under the condition of fixed Nb5+ concentration regulating Sm3+ concentration and fixed Sm3+ concentration regulating Nb5+ concentration were obtained respectively. By further fitting the emission decay curves of Sm3+ under two conditions, the decreasing average lifetime is obtained. Thermal stability tests of the samples also hinted the presence of such energy transfer. This regular change can provide a good reference for developing new self-activated phosphors.

Er3+/Tm3+ codoped CaF2 based oxyfluoroborosilicate glass-ceramics for fiber laser applications

Transparent Er3+/Tm3+ codoped CaF2 based oxyfluoroborosilicate glass-ceramics (BSEr1TmxGCs) with variable Tm3+ concentration were prepared through melt quench process followed by reheat treatment at 450 °C/1h. They were characterized through differential scanning calorimetry (DSC), powder X-ray diffraction (XRD), Fourier transform infrared (FTIR) Raman spectroscopy, near infrared (NIR) emission and luminescence decay. The formation of CaF2 nanocrystallites against oxyfluoroborosilicate glassy phase was confirmed by scanning electron microscopic (SEM) and hi-resolution transmission electron microscopic (HRTEM) studies. The NIR emission properties were investigated at 460 nm diode laser pumping. The applicability of BSEr1TmxGCs were examined by evaluating effective bandwidth (Δλeff), stimulated emission cross-section (σe), gain bandwidth (σe × Δλeff), figure of merit (σe × τR) and quantum efficiency (ηQE). The energy transfer efficiency (ηET), rate of energy transfer (WET) between Er3+ and Tm3+ and the rate of non-radiative transitions (WNR) were also calculated. The comparative NIR emission performance suggests that the BSEr1Tm1GC has proficiency for 1530 nm broadband fiber lasers and optical amplifiers in short wavelength and conventional wavelength (S + C) band communication window.

Synthesis of low-dimensional metal halide CsAgCl2 for X-ray scintillation applications

Low-dimensional metal halides, which possess efficient luminescent properties, have garnered significant interest in the fields of optoelectronics and radiation detection. This study introduces novel lead-free silver-based metal halide material, CsAgCl2 microcrystals (MCs). These MCs have a one-dimensional atomic chain structure and a unique [AgCl5]4- tetragonal shared triangular configuration. CsAgCl2 MCs exhibit excellent performance as X-ray scintillators due to their bright broadband yellow emission and fast decay time in the microsecond range. The large Stokes shift of 350 nm is produced by self-trapped exciton emission. In X-ray scintillation applications, CsAgCl2 MCs demonstrate a high light yield of 13280 photons/MeV and a wide range of linear scintillation response. It is noteworthy that the CsAgCl2 MCs maintain good stability under both atmospheric conditions and continuous X-ray irradiation. The sample was used in an X-ray imaging screen, which clearly presented the X-ray projection image of a wooden stick. As a result, this research not only contributes to the collection of lead-free metal halide scintillators but also indicates that CsAgCl2 MCs have a wide range of future applications and potential in areas such as medical imaging, scientific research, and diagnostic and detection technologies.

Concentration- and temperature-dependent luminescence mechanisms and fluorescence dynamic temperature sensing of NaY(MoO4)2:Tb3+ phosphors

High-temperature solid-state reaction technique was used to prepare NaY(MoO4)2:Tb3+ phosphors with different Tb3+ concentrations. XRD patterns showed that the prepared samples contained only single-phased compound NaY(MoO4)2. The concentration-dependent green luminescent intensity of Tb3+ was studied, and it was found that the concentration quenching process is in charge of Ozawa's model. The concentration-effect of luminescence decay of 5D4 level was explained by the Auzel's self-generated quenching theory. Starting from the Reisfeld's theory, the analysis on the luminescence decays also indicated exchange interaction was responsible for the concentration quenching. Temperature dependences of the green emission intensity and decay were comprehended based on the crossover mechanism. A novel temperature sensing technique rooting in the fluorescence dynamics of 5D4 level of Tb3+ in NaY(MoO4)2 was proposed, and the absolute and relative sensitivities were deduced and assessed.

Blue and white light emissions and energy transfer in Tm3+ and Dy3+/Tm3+ doped lithium-aluminum-zinc phosphate glasses

Lithium-aluminum-zinc phosphate glasses doped with thulium and dysprosium ions are characterized by using spectroscopy techniques. The Judd-Ofelt parameters were evaluated to calculate the radiative parameters of thulium 1D23F4 and 1G43H6 visible transitions and 3H43F4 near infrared transition, which shows the highest optical amplification parameters. Upon 356 nm excitation, the Tm3+ doped phosphate glass emits blue light with CIE1931 chromaticity coordinates x = 0.1540 and y = 0.0283 and color purity around 96.8%. With excitations at 347 and 350 nm, the Dy3+/Tm3+ doped phosphate glass emits neutral and cold white light with correlated color temperature values of 4716 and 6628 K, respectively. The dysprosium emission decay time in the codoped glass is shorter than that in the Dy3+ single-doped glass, indicating a non-radiative energy transfer from Dy3+ to Tm3+. The dominant electrical interaction involved in the energy transfer, following the model Inokuti-Hirayama, is of dipole-dipole type. The energy transfer probability and efficiency are 769.0 s-1 and 0.53, respectively. Tm3+ doped and Dy3+/Tm3+co-doped lithium-aluminum-zinc phosphate glasses could be appropriate for blue and neutral/cold white light-emitting device applications.

Hard X-ray nanoprobe to study the emission properties of Ce-doped YAG wafer by using XEOL and TR-XEOL

In this study, the valent state, emission properties, and decay lifetime of Ce-doped yttrium aluminum garnet (Y3Al5O12, YAG) wafer have been probed using X-ray absorption (XAS), X-ray excited optical luminescence (XEOL), and time-resolved XEOL (TR-XEOL). The XAS spectrum demonstrates that Ce ions are in the trivalent state, and the XEOL spectrum exhibits typical 5 d1-4f1(2F5/2) and 5 d1-4f1(2F7/2) transitions of Ce3+ ions, with emission peaks at ∼528 nm and 582 nm, respectively. From the TR-XEOL measurements, the decay lifetimes of 5 d1-4f1(2F5/2) and 5 d1-4f1(2F7/2) transitions are about ∼90 ns and ∼100 ns, respectively. We found that the reabsorption effects will not only make the 5 d1-4f1(2F7/2) transitions have longer decay lifetime, but also the higher emission intensity. By comparison with photoluminescence (PL) and time-resolved PL using a pulsed laser at 375 nm, we found that the emission spectra and decay lifetime of Ce-doped YAG (111) wafer are different when using X-ray irradiation. The longer decay lifetime measured by TR-XEOL compared TR-PL are caused by high X-ray dose irradiation. In addition, high X-ray doses provided by the nano-focus X-ray beam will be influenced the emission behaviors of Ce-doped YAG (111) wafer. Which phenomena have been demonstrated by using time-dependent XEOL with irradiation for 10 h. These peculiar emission behaviors observed with a hard X-ray nanoprobe may be able to provide important information on quantum technologies and scintillators used in hard X-ray detectors.

Spectral deconvolution approach for Beryllium-7 detection: Evaluating soil redistribution with NaI(Tl) detectors

Beryllium-7 is a cosmogenic radionuclide produced in the upper atmosphere through the spallation of cosmic rays and falls to Earth mainly by wet deposition. Given its short half-life (53 days) and strong adsorption to the clay present in the soil, 7Be inventory can be evaluated to obtain information about soil redistribution over periods of up to 6 months. By performing these measurements, one can infer the efficiency of soil management and conservation procedures. The isotope presence is measured using gamma-ray spectrometry to detect its decay emission, specifically a photon with an energy of 477.6 keV. Since other isotopes found in soil emit photons with similar energies, it is common to use High-Purity Germanium (HPGe) detectors due to their high energy resolution. However, these detectors are expensive and require cryogenic cooling during operation. An alternative is the Thallium-Activated Sodium Iodide (NaI(Tl)) detector, which is less costly and does not require cryogenic cooling, but has poorer resolution and cannot separate the emissions from 228Ac (463.0 keV), 7Be, and 208Tl (510.7 keV). This work aims to apply spectral deconvolution to quantify 7Be in soil samples collected from an agricultural mega-parcel situated on a hill slope and evaluate the soil redistribution experienced within. The activities of the interfering isotopes were quantified using other emissions, and the results were used to calculate the corresponding area in the desired region of the spectra. From this, 7Be activities were calculated and compared with the HPGe results to validate the deconvolution technique. The calculated activities for the three radioisotopes showed similar correspondence between the two detectors, indicating that the applied method is adequate for evaluating soil redistribution at lower costs. The calculated net soil deposition was 36.4 ± 6.4 kgm−2 for the NaI(Tl) detector and 26.4 ± 7.9 kgm−2 for the HPGe detector during the evaluated period. Furthermore, these results suggest that a similar approach can be applied to quantify other isotopes using NaI(Tl) detectors as an alternative to HPGe detectors.

Hybrid metal halide family with color-time-dual-resolved phosphorescence for multiplexed information security applications

Luminescent materials with engineered optical properties play an important role in anti-counterfeiting and information security technology. However, conventional luminescent coding is limited by fluorescence color or intensity, and high-level multi-dimensional luminescent encryption technology remains a critically challenging goal in different scenarios. To improve the encoding capacity, we present an optical multiplexing concept by synchronously manipulating the emission color and decay lifetimes of room-temperature phosphorescence materials at molecular level. Herein, we devise a family of zero-dimensional (0D) hybrid metal halides by combining organic phosphonium cations and metal halide tetrahedral anions as independent luminescent centers, which display blue phosphorescence and green persistent afterglow with the highest quantum yields of 39.9 % and 57.3 %, respectively. Significantly, the luminescence lifetime can be fine-tuned in the range of 0.0968–0.5046 μs and 33.46–125.61 ms as temporary time coding through precisely controlling the heavy atomic effect and inter-molecular interactions. As a consequence, synchronous blue phosphorescence and green afterglow are integrated into one 0D halide platform with adjustable emission lifetime acting as color- and time-resolved dual RTP materials, which realize the multiple applications in high-level anti-counterfeiting and information storage. The color-lifetime-dual-resolved encoding ability greatly broadens the scope of luminescent halide materials for optical multiplexing applications.

Ln3+ Induced Thermally Activated Delayed Fluorescence of Chiral Heterometallic Clusters Ln2Ag28.

A series of TADF-active compounds: 0D chiral Ln-Ag(I) clusters L-/D-Ln2Ag28-0D (Ln=Eu/Gd) and 2D chiral Ln-Ag(I) cluster-based frameworks L-/D-Ln2Ag28-2D (Ln=Gd) has been synthesized. Atomic-level structural analysis showed that the chiral Ag(I) cluster units {Ag14S12} in L-/D-Ln2Ag28-0D and L-/D-Ln2Ag28-2D exhibited similar configurations, linked by varying numbers of [Ln(H2O)x]3+ (x=6 for 0D, x=3 for 2D) to form the final target compounds. Temperature-dependent emission spectra and decay lifetimes measurement demonstrated the presence of TADF in L-Ln2Ag28-0D (Ln=Eu/Gd) and L-Gd2Ag28-2D. Experimentally, the remarkable TADF properties primarily originated from {Ag14S12} moieties in these compounds. Notably, {Ag14S12} in L-Eu2Ag28-0D and L-Gd2Ag28-2D displayed higher promote fluorescence rate and shorter TADF decay times than L-Gd2Ag28-0D. Combined with theoretical calculations, it was determined that the TADF behaviors of {Ag14S12} cluster units were induced by 4 f perturbation of Ln3+ ions. Specially, while maintaining ΔE(S1-T1) small enough, it can significantly increase k(S1→S0) and reduce TADF decay time by adjusting the type or number of Ln3+ ions, thus achieving the purpose of improving TADF for cluster-based luminescent materials.

Ln3+ Induced Thermally Activated Delayed Fluorescence of Chiral Heterometallic Clusters Ln2Ag28

AbstractA series of TADF‐active compounds: 0D chiral Ln−Ag(I) clusters L‐/D‐Ln2Ag28‐0D (Ln=Eu/Gd) and 2D chiral Ln−Ag(I) cluster‐based frameworks L‐/D‐Ln2Ag28‐2D (Ln=Gd) has been synthesized. Atomic‐level structural analysis showed that the chiral Ag(I) cluster units {Ag14S12} in L‐/D‐Ln2Ag28‐0D and L‐/D‐Ln2Ag28‐2D exhibited similar configurations, linked by varying numbers of [Ln(H2O)x]3+ (x=6 for 0D, x=3 for 2D) to form the final target compounds. Temperature‐dependent emission spectra and decay lifetimes measurement demonstrated the presence of TADF in L‐Ln2Ag28‐0D (Ln=Eu/Gd) and L‐Gd2Ag28‐2D. Experimentally, the remarkable TADF properties primarily originated from {Ag14S12} moieties in these compounds. Notably, {Ag14S12} in L‐Eu2Ag28‐0D and L‐Gd2Ag28‐2D displayed higher promote fluorescence rate and shorter TADF decay times than L‐Gd2Ag28‐0D. Combined with theoretical calculations, it was determined that the TADF behaviors of {Ag14S12} cluster units were induced by 4 f perturbation of Ln3+ ions. Specially, while maintaining ΔE(S1–T1) small enough, it can significantly increase k(S1→S0) and reduce TADF decay time by adjusting the type or number of Ln3+ ions, thus achieving the purpose of improving TADF for cluster‐based luminescent materials.

New Insights in Luminescence and Quenching Mechanisms of Ag2S Nanocrystals through Temperature-Dependent Spectroscopy.

Bright near-infrared-emitting Ag2S nanocrystals (NCs) are used for in vivo temperature sensing relying on a reversible variation in intensity and photoluminescence lifetime within the physiological temperature range. Here, to gain insights into the luminescence and quenching mechanisms, we investigated the temperature-dependent luminescence of Ag2S NCs from 300 to 10 K. Interestingly, both emission and lifetime measurements reveal similar and strong thermal quenching from 200 to 300 K, indicating an intrinsic quenching process that limits the photoluminescence quantum yield at room temperature, even for perfectly passivated NCs. The low thermal quenching temperature, broadband emission, and multiexponential microsecond decay behavior suggest the optical transition involves strong lattice relaxation, which is consistent with the recombination of a Ag+-trapped hole with a delocalized conduction band electron. Our findings offer valuable insights for understanding the optical properties of Ag2S NCs and the thermal quenching mechanism underlying their temperature-sensing capabilities.